In one aspect, the present invention relates to backfills for use in areas where excavations are made in wet soil conditions and where the excavated soil is unsuitable for returning to the excavation. In another aspect, the present invention relates to backfill material for surrounding grounding members to increase their long term efficiency and increase their ability to transmit a current to the ground. More particularly, the present invention relates in its first aspect to a method for stabilizing wet soil that is incapable of being readily compacted, generally referred to as over-optimum soil, to yield a relatively dry, compactable soil mass for returning to an excavation from which the wet soil was removed. Furthermore, the present invention relates in its second aspect to a method and composition for providing a fill material for surrounding grounding members, such as an anode of a cathodic protection system.
Wet soil, containing on the order of 10% to 40% by weight of water, based on the wet soil, is generally unsuitable for backfilling into an excavation from which it has been taken because it will not readily compact to a degree sufficient to support a load. Depending upon the type of soil, soil containing less than 10% water may also be unsuitable for backfill. Moreover, wet soil, because it will not compact, tends to settle over a period of time after it has been replaced in an excavation, thus causing a ground depression at the location of the excavation. Conventionally, this compactability problem is solved by removing the wet soil from the excavation location and by transporting to the excavation location a dry, compactable backfill such as a relatively dry sand or other soil composition. Although this method of backfilling excavation works well, it can be expensive and time consuming, especially when the transportation costs of the replacement backfill are taken into consideration.
When no replacement backfill is available or when it is extremely expensive to transport dry, compactable backfill to the excavation location, drying agents have been employed in an attempt to sufficiently reduce the apparent water content of the soil so that the soil can be replaced in the excavation from which it was taken and compacted to a degree that will support a load and will not settle to any significant degree with time. One such drying agent is lime. Lime has been employed as a drying agent in both quicklime and hydrated form. Although quicklime has a greater affinity for water, it is normally not used as a drying agent because of its caustic nature. When the soil to be dried is relatively wet, on the order of 25% or more water, hydrated must be used in large quantities to achieve a sufficient degree of dryness within a short period of time for the soil to be compacted. Such large quantities of lime are expensive and create secondary problems. When such large quantities of lime are used, the soil/lime mass becomes very dusty and difficult to handle, the dusty material is somewhat hazardous to the laborers handling the backfill, and the resulting soil mass tends to dry out and crack with time and furthermore becomes so hard that it cannot be easily worked. Thus, combining large quantities of lime with the soil has been an unsatisfactory solution for rapid stabilization.
The amount of lime required to dry out the soil can be reduced by using quicklime. However, as previously pointed out, quicklime is extremely caustic and thus difficult to handle, especially where medium to large quantities are required. Furthermore, large quantities of quicklime are required to achieve rapid drying of the soil, compounding the problems associated with handling and safety. Also, when large quantities of lime are used, excessive amounts of undesirable heat are generated in the hydration process. The soil mass resulting from the use of large quantities of lime can become quite hard after compaction, resulting in an overload on a pipe on which the backfill is placed and resulting in a soil mass that is difficult to reexcavate.
Accordingly, it is a broad object of the present invention to provide a soil additive for stabilizing wet soil, that is, to produce a relatively dry, compactable soil mass for use as a backfill. Further objects of the present invention are to eliminate the need to transport replacement backfill to the location of an excavation and thus reduce the manual labor and expense required in replacing wet backfill; to eliminate the dust problem by reducing the amount of additive required to dry out the soil; and to provide methods and compositions that are easily handled by laborers normally replacing the backfill and that do not require any substantial learning curve to handle readily and efficiently.